Most present-day switching-type power supplies include a sensing circuit for providing fold-back current limiting to the power supply in order to prevent the power supply from self-destructing in the event that a current or voltage overload occurs. One such current fold-back circuit is described, for example, in U.S. Pat. No. 4,128,866.
The prior art current fold-back circuits, however, for the most part, sense only the local output current of the power supply. This means that the current sensing level must be adjusted every time the output voltage of the power supply is adjusted. If such an adjustment is not made to the current sensing level in the prior art sensing circuits, the limit current at which current fold-back occurs rises when the output voltage is increased and drops when the output voltage is decreased.
The current fold-back circuit of the present invention corrects the problem by sensing the voltage across the power supply potentiometer which is used to adjust output voltage, and accordingly the circuit of the invention serves to maintain the current limiting point virtually constant as the output voltage is adjusted.
When the power supply is connected to a remote load through a bus, the remote current sense point increases depending upon the resistance of the bus. This can create a situation in that short circuits in the load are undetected. The circuit of the present invention also senses the voltage across the remote load so as to maintain the current limiting point essentially constant regardless of bus-to-load resistance.